476 THE ANNELIDA POLYCHAETA. 



i. Branchiae without dorsal appendages; tube free, open at botli ends; operculum 

 conic, terminated by a flat plate covered with concentric striae. 



Diirupa Berkeley. 

 a. Branchiae with dorsal appendages; tube fixed; operculum glandiform. 



Dasynema St. Joseph. 

 hh. No thoracic membrane; operculum membranous and vesicular. 



Hyalopomatus Marenzeller. 

 gg. Abdominal setae in the form of stout, moderately curving, aciculiform spines on all 

 but the posterior somites, where they are replaced by very long, fine capillary setae 

 which are straight. 



Operculum obconic, without processes Paumotella, gen. nov. 



cc. Uncini with teeth fewer and coarser, the series terminating anteriorly, or below, in a tooth larger 

 than the others but similarly pointed. 

 d. No operculum. 



Setae of the first thoracic somite geniculate and with tip preceded by a posterior notch 



and crenulate wng; abdominal setae capillary Protis Ehlers. 



dd. With an operculum. 



e. Operculum formed by the transformation of only the tip of one or more branchiae. 



/. Collar setae geniculate; operculum with a horny plate Protoplacoslegus Bush. 



//. Collar setae not geniculate; operculum with a calcareous plate. 



Josephella CauUery and Mesnil. 

 ee. Operculum formed by the transformation of one or more entire branchiae. 

 /. Operculum without radii. 



g. Operculum forming two deep funnels one above the other, with the edge subdivided 



into branched processes Schizocraspedon Bush. 



dd. Operculum forming a deep funnel with edge incised and each process terminating in a knob; 



a long curved process arising from the center of the funnel Glossopsis Bush. 



//. Operculum with radii. 



g. Peduncle of operculum bearing four digitiform processes in the form of a cross. 

 Operculum infundibuliform, crenulate, rays ending in conic teeth. 



Crucigera Benedict. 

 gg. Peduncle of operculum not bearing such processes. 

 h. Operculum at middle with a crown of spines or rods. 

 i. Spines of crown simple and regularly tapered, without lateral processes. 



Eupomalus Philippi. 

 ii. Spines of crown with lateral processes. 



j. Spines pointed Hydroides Gunnerus. 



ij. Spines blunt, each with a single lateral process on each side. .Eucarphus Morch. 

 hh. Operculum \vith no such crown of spines. 



i. Radii of operculum nmncrous, margin serrate Serpula Linnc. 



ii. Radii of operculum few, margin crenate Sclerostyla Morch. 



Because of a marked variability in many of the more obvious characters 

 of tliis family their classification is attended with many difficulties through 

 which no royal road has been discovered. The most definite and least variable 

 characters are those afforded by the setae, the study of which along lines indi- 

 cated by the work and experience of Claparede, Langerhans, Marenzeller, and 

 St. Joseph seems to yield the only satisfactory basis for a classification giving 

 promise of preciseness and naturalness. Any arrangement made at present 

 must be incomplete, and in considerable measure tentative, because of nmnerous 

 gaps in our knowledge even of the known forms. The account of the setae, and 

 particularly of the uncini, where not omitted altogether, is in many descrip- 

 tions wholly inadequate. In the analysis of genera given in the preceding 



